A year and a half after the federal Liberals hitched their ship to a carbon-reduction policy - and then sank deep in the waters of popular support - Leader Michael Ignatieff is hoping a revamped environmental plan will raise his party's fortunes.

One of the first detailed policies outlined by the party under Mr. Ignatieff, the plan unveiled Thursday is not a tax on carbon-based fuels of the sort proposed by his predecessor Stéphane Dion. The former Liberal leader's Green Shift concept was mocked by Conservatives as being "a tax on everything" and ultimately cost the Liberals heavily at the polls.

Instead, Mr. Ignatieff's proposal is a multifaceted attack on greenhouse gases that includes investments in green energy, a cap-and-trade system, the toughest standards for vehicle emissions in North America, new legislation to co-ordinate national environmental efforts - and one unanswered question.

The Conservative government has said it will reduce greenhouse-gas emissions by 20 per cent below 2006 levels by 2020.

Mr. Ignatieff said he would instead set 1990 as the base year - a marker adopted by the European Union. What he did not spell out is the size of decrease he would impose. Instead, he said, the reductions must keep global warming to 2 degrees Celsius above pre-industrial levels.

Critics in other parties jumped on the absence of hard numbers in the Liberal proposal.

"It has no target in it whatsoever so I don't know how one could call it a plan under any stretch of the imagination," said Jim Prentice, the federal Environment Minister. "Everyone else in the world has been arriving at commitments on targets."

Bloc Québécois Leader Gilles Duceppe pointed out that earlier this week the Liberals voted for a Bloc motion that called for a reduction of greenhouse-gas emissions by 25 per cent below 1990 levels by 2020. "They supported it and now they don't remember it," Mr. Duceppe said. "It's a little bit bizarre."

Mr. Ignatieff said his plan is to raise the bar - but he cannot do that without international consensus.

"That is what you go to Copenhagen to talk about," he said. "Because you've got to have realistic targets, you've got to have attainable targets. This is no time to pick numbers out of the air. And you've got to do that with other industrial countries."

The key, said Mr. Ignatieff, is that the targets must be set to 1990.

A recent report by the economic modelling firm M.K. Jaccard and Associates found that Canada could meet a 2020 target to reduce greenhouse-gas emissions below 1990 levels while preserving economic growth, but that to do so would be deeply disruptive to the economy and very expensive.

Mr. Ignatieff also said he would quickly introduce a cap-and-trade system that allows industries that emit more carbon than permitted by law to buy carbon credits from those that emit less. "You pollute, you pay," he told an audience at Laval University in Quebec City.

The Conservatives have said they want to introduce a continent-wide cap-and-trade system between 2012 and 2015.

Mr. Ignatieff said Canada's system must be compatible with that of the United States "but that does not mean - and this is key - that we have to wait for Washington to move forward."

The Liberal Leader also promised that if his party wins the next election, money would be spent on renewable energy, greener transit systems and the development of a new green economy.